Vegetable oils and animal fats can be transesteried to biodiesel with alcohol for use as an alternative to diesel fuel. This chapter deals mahua oil, its transfer into different esters, their performance and emission characteristics in a four-stroke, direct injection diesel engine. The results showed that the thermal efciency was high in the case of the methyl ester compared to other esters and to diesel fuel. The tail-pipe emissions and noise levels were lower in the case of the methyl ester, compared to those of diesel and other esters. The methyl ester dominated other esters on the basis of engine performance and emissions and can be used as an alternative fuel for existing diesel engines.